5E is far more forgiving than AD&D was. Fortunately, it's also equally amenable to Combat As War and player-controlled pacing.
'Amenable?' It certainly isn't robust to it, class balance depending heavily on pacing.
I did find pemerton's insight about player-controlled pacing and 'CaW' interesting. I'm not sure if I'm convinced, but it's interesting.
The scaling I am referring to is of mechanical scaling that goes to the basics of action resolution. In AD&D, AC and damage per hit do not vary very much with level
OK, scaling with level, vs Hemlock talking scaling with numbers of foes on one side. Not scaling with level (like BA) means numbers tell more heavily. So, yeah, OK...
What this means is that, in AD&D, a player-side approach of trying to manage the pacing of events so that even high HD foes can be taken down in ones and twos is viable; whereas in other editions, even 5e with its bounded accuracy, this involves greater risk.
Well, numbers tell heavily in 5e, so you should be able to take on a lone enemy of higher CR with healthy chance of success (though maybe, because of the significant damage scaling, not without PCs being dropped). In 3e that wasn't so much an option because basics like AC scaled, while in 4e a lone higher-level enemy could be translated to a solo 9 levels lower.
The rest period is a week.
And it was part of an optional alternative to simply death at 0 hps.
This is not any sort of criticism of 5e. But I think it contributes to the explanation of why 5e is thought to need more involved encounter-building guidelines than AD&D does.
I has more involved encounter building guidelines than 4e did or 3.5/PF does, but AD&D didn't really have such guidelines, at all, at least, not explicit & formulaic enough to be characterized as 'more involved.'
More art than science, certainly... and more Picasso than Rembrandt.
All this discussion makes me wonder what these guidelines are actually for?
Are they really for a DM running their own campaign?
Yes.
Or are they for adventure creators looking to align their adventure with a particular level
Yes. HotDQ could sure have benefited from them.
in order to making running that adventure easy for a DM at any skill level?
I doubt any guidelines could be that good in this context.
I think these guidelines are really for the latter. An experienced DM running a game for their own players will gain an understanding of what constitutes a suitable challenge for their table. No published guidelines are going to be better than that.
True, once that rapport is established, but they can be a useful tool, none the less. They could also be useful to the DM running one-offs or with a varied roster of players, where 'knowing your players' is less of an option.
Encounter guidelines also serve as the foundation that allowed 5e to deliver the promised 'crystal clear guidance' about encounters/day (and, it turns out short rests/day) around which the classes were designed to balance. So there's that, too.
The bottom line is that, like just about everything else in 5e, the DM can use those guidelines as a starting point from which to make the game his own. You're presented with a game that you can make
better, rather than one you might fear making worse.
Bottom line: 5E combat doesn't resemble cinematic combat. It's over too quickly.
D&D combat can resemble cinematic combat (or 'have a cinematic feel'), depending on edition, and, particularly upon how you visualize 'hits' and hps (and the restoration of same)... 4e tended to get very cinematic, including in ways that some people reacted very poorly too. 5e 'fast combat,' can be less so, sure, in both senses.